Shape v's Cut
Lapidary is the term used to describe forming rough stones, minerals and gemstones (other than diamonds) into a finished shape suitable for use in a piece of jewellery. As cutting diamonds requires an expert who uses complex techniques learned over many years of training, the person possessing these skills is called a ‘gem cutter’ or ‘diamond cutter’.
Shape refers to the overall form of a cut stone when viewed from above.
Cut refers to the way the stone is faceted.
The ‘square cut’ and ‘princess cut’ forms are both square shaped when viewed from above, but the number and placement of the facets is quite different. The same is true of the ‘octagon cut’ and the ‘emerald cut’, same shape, different cut.
The classic diamond shape is the brilliant round cut. It has either 57 or 58 facets, depending upon whether the culet (the bottom of the stone) is faceted or left untouched. The very top face of the gem is called the ‘table’, the widest point is called the girdle, above the girdle is the crown and below is the pavilion.
In choosing the cut to be applied to a gemstone, the cutter will examine the rough stone for inclusions so that he can eliminate or position them in the final cut for the best result. Other factors that decide which cut is most appropriate include the fitting for which it is intended, the shape of the uncut stone and the ability to retain the highest percentage of carat weight.
Any cut other than the ‘round brilliant’ is called a fancy cut. Some of the more popular faceted fancy cuts include: princess, asscher, cushion, emerald, heart, oval, marquise, pear, radiant, baguette, octagon and trillion. A cabochon is not faceted; it has a flat bottom and a domed top.
The princess cut is similar to the round brilliant except it is a perfect square with between 57 and 70 facets. The corners must not be rounded and this design is implemented to get the maximum brilliance from a square shaped stone.
The asscher cut, also known as the square emerald cut is a stepped design. It features 58 facets and a higher crown and a smaller table than an emerald cut stone. The corners are cropped which can give the stone the appearance of being octagonal when not mounted in a four prong setting.
The emerald cut has a large table and displays colours within the stone very dramatically. Most emerald cut stones have around 50 stepped facets, in a shape that ranges between nearly square to rectangular. This cut shows light and dark, rather than the sparkle and fire of a brilliant cut stone.
Cushion cut stones feature around 64 facets that maximise the lustre of the gem. The table has eight sides and the girdle has rounded corners and sides. It is similar in shape to an oval cut, but the curvature of the ends and sides is much less, giving a squarer look.
Emerald cut gemstones are rectangular in shape with cut corners and stepped facets. Normally these stones have a proportion where the length is close to 1.5 times the width and feature around 50 facets. Equidistant steps on the pavilion is the primary difference between this and the octagon cut style.
Heart cut stones typically have 59 facets and are just slightly longer than they are wide. This cut is based on the pear cut with a cleft at the top end. Frequently set in rings, but also common in pendants and earrings with sales peaking (surprisingly) around St. Valentine’s day each year.
The Oval cut displays great fire when well proportioned; the length should be approaching one and one half times the width of this stone for best effect. Like most round cut stones, this cut is based on the round brilliant and has around 56 facets.
Marquise cut gems are similar in shape to an American football. A long oval shape with pointed ends. There is a range of length to width ratios from (very technical here) skinny to fat. Most people prefer a stone with the length around twice the width.
Pear cut stones are similar in shape to a tear drop and display lots of fire and sparkle. 57 facet cuts are common in this combination marquise and oval style of cut. One problem with this cut is the potential for a ‘bow tie’ effect to be seen; a dark patch within the stone that looks like a bowtie.
Radiant cut stones are faceted to produce the most fire from within. Similar in shape to the emerald cut with cropped corners they range from square to rectangular. Featuring a large table this cut is more forgiving on stones with defects than an emerald cut would be.
Baguette cut gems are normally rectangular in shape, but a tapered variation is also common where the length of the two shortest sides is uneven. This shape is step cut with 14 to 20 facets and is considered to be the forerunner to the emerald cut style which has around 50 facets.
Octagon cut styles have 53 facets step cut with cropped corners. The difference between this cut and emerald cut is that the steps on the pavilion are not equidistant.
Trillion cut gems are triangular in shape usually with 43 facets that display plenty of colour and light. Best for light coloured gemstones where a stones brilliance can be maximized, but some darker stones including amethyst are cut in this manner to make them appear lighter and brighter.
A Cabochon is an un-faceted stone. It has a flat bottom and a domed
top and is most often used for opaque gems, but star sapphires and star
rubies (stones with asterism) are also frequently cut in this style.
Most cabochons are elliptical (oval) in shape although circles, hearts
and other shapes can be created.